<!DOCTYPE html>
<html>

<head>
    <meta charset="utf-8" />
    <title>地狗购物网——网页定位导航效果</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }
        html,body{
            height: 100%;
        }
        body {
            font-size: 12px;
            line-height: 1.7;
        }

        li {
            list-style: none;
        }

        #content {
            width: 800px;
            margin: 0 auto;
            padding: 20px;
        }

        #content h1 {
            color: #0088bb;
        }

        #content .item {
            padding: 20px;
            margin-bottom: 20px;
            border: 1px dotted #0088bb;
        }

        #content .item h2 {
            font-size: 16px;
            font-weight: bold;
            border-bottom: 2px solid #0088bb;
            margin-bottom: 10px;
        }

        #content .item li {
            display: inline;
            margin-right: 10px;
        }

        #content .item li a img {
            width: 230px;
            height: 230px;
            border: none;
        }

        #menu {
            position: fixed;
            top: 100px;
            left: 50%;
            margin-left: 400px;
            width: 80px;
        }

        #menu ul li a {
            display: block;
            margin: 5px 0;
            font-size: 14px;
            font-weight: bold;
            color: #333;
            width: 80px;
            height: 50px;
            line-height: 50px;
            text-decoration: none;
            text-align: center;
        }

        #menu ul li a:hover,
        #menu ul li a.current {
            color: #fff;
            background: #0088bb;
        }

        /*ie6 hack*/
        * html,
        * html body {
            background-image: url(about:blank);
            background-attachment: fixed;
        }

        * html #menu {
            /*position: fixed;*/
            position: absolute;
            top: expression(((e=document.documentElement.scrollTop)?e:document.body.scrollTop)+100+'px');
        }
    </style>
    <script>

        //定义getByClassName函数，让函数实现根据class name获取对象并返回
        function getByClassName(obj, cls) {
            var elements = obj.getElementsByTagName("*");
            var result = [];
            for (var i = 0; i < elements.length; i++) {
                if (elements[i].className == cls) {
                    result.push(elements[i]);
                }
            }
            return result;
        }

        function hasClass(obj, cls) {
            return obj.className.match(new RegExp("(\\s|^)" + cls + "(\\s|$)"));
        }

        function removeClass(obj, cls) {
            if (hasClass(obj, cls)) {
                //remove
                var reg = new RegExp("(\\s|^)" + cls + "(\\s|$)");
                obj.className = obj.className.replace(reg, "");
            }
        }


        // //定义 addClassName函数，让函数实现给对象增加class 
        function addClassName(obj, cls) {
            if (!hasClass(obj, cls)) {
                obj.className += " " + cls;
            }
        }

        window.onload = function () {

            window.onscroll = function () {
                var top = document.documentElement&&document.documentElement.scrollTop ? document.documentElement.scrollTop : document.body.scrollTop;
                var menus = document.getElementById("menu").getElementsByTagName("a");
                // console.log(document.body.scrollTop);
                var items = getByClassName(document.getElementById("content"), "item");

                var currentId = "";

                for (var i = 0; i < items.length; i++) {
                    var _item = items[i];
                    var _itemTop = _item.offsetTop;
                    
                    if (top > _itemTop - 200) {
                        currentId = _item.id;
                    } else {
                        break;
                    }
                }


                //请补充此处代码，给正确的menu下的a元素class赋值current
                if (currentId) {
                    for (var i = 0; i < menus.length; i++) {
                        var menu = menus[i];
                        var _hrefArray = menu.href.split("#");
                        var _hreflink = _hrefArray[_hrefArray.length - 1];
                        // console.log(currentId);
                        if (currentId != _hreflink) {
                            removeClass(menu, 'current');
                        }
                        else {
                            addClassName(menu, 'current');
                        }
                    }
                }



            }
        }	
    </script>
</head>

<body>
    <div id="menu">
        <ul>
            <!--运用锚点，实现导航定位。-->


            <li><a href="#item1" class="current">1F 男装</a></li>
            <li><a href="#item2">2F 女装</a></li>
            <li><a href="#item3">3F 美妆</a></li>
            <li><a href="#item4">4F 数码</a></li>
            <li><a href="#item5">5F 母婴</a></li>
        </ul>
    </div>
    <div id="content">
        <h1>地狗购物网</h1>

        <div id="item1" class="item">
            <h2>1F 男装</h2>
            <ul>
                <li><a href="#"><img src="http://img.mukewang.com/53660fce0001111903990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/53660fce0001111903990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/53660fce0001111903990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/53660fce0001111903990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/53660fce0001111903990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/53660fce0001111903990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/53660fce0001111903990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/53660fce0001111903990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/53660fce0001111903990422.jpg" alt="" /></a></li>
            </ul>
        </div>
        <div id="item2" class="item">
            <h2>2F 女装</h2>
            <ul>
                <li><a href="#"><img src="http://img.mukewang.com/5366104c0001e5c403990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/5366104c0001e5c403990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/5366104c0001e5c403990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/5366104c0001e5c403990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/5366104c0001e5c403990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/5366104c0001e5c403990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/5366104c0001e5c403990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/5366104c0001e5c403990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/5366104c0001e5c403990422.jpg" alt="" /></a></li>
            </ul>
        </div>
        <div id="item3" class="item">
            <h2>3F 美妆</h2>
            <ul>
                <li><a href="#"><img src="http://img.mukewang.com/536610820001cf5b03990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/536610820001cf5b03990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/536610820001cf5b03990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/536610820001cf5b03990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/536610820001cf5b03990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/536610820001cf5b03990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/536610820001cf5b03990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/536610820001cf5b03990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/536610820001cf5b03990422.jpg" alt="" /></a></li>
            </ul>
        </div>
        <div id="item4" class="item">
            <h2>4F 数码</h2>
            <ul>
                <li><a href="#"><img src="http://img.mukewang.com/536610ac00012df703990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/536610ac00012df703990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/536610ac00012df703990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/536610ac00012df703990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/536610ac00012df703990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/536610ac00012df703990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/536610ac00012df703990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/536610ac00012df703990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/536610ac00012df703990422.jpg" alt="" /></a></li>
            </ul>
        </div>
        <div id="item5" class="item">
            <h2>5F 母婴</h2>
            <ul>
                <li><a href="#"><img src="http://img.mukewang.com/536610cd0001f34603990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/536610cd0001f34603990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/536610cd0001f34603990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/536610cd0001f34603990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/536610cd0001f34603990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/536610cd0001f34603990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/536610cd0001f34603990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/536610cd0001f34603990422.jpg" alt="" /></a></li>
                <li><a href="#"><img src="http://img.mukewang.com/536610cd0001f34603990422.jpg" alt="" /></a></li>
            </ul>
        </div>
    </div>
</body>

</html>